Introduction

A
TileOverlay defines a set of images that are added on top of
the base map tiles.

You need to provide the tiles for each zoom level that you want to support.
If you have enough tiles at multiple zoom levels, you can supplement Google's
map data for the entire map.

Tile overlays are useful when you want to add extensive imagery to the map,
typically covering large geographical areas. In contrast,
ground overlays
are useful when you wish to fix a single image at one area on the map.

You can also use transparent tile overlays to add extra features to the map,
by setting a transparency factor on the tile overlay programmatically or by
providing transparent tile images.

Tile coordinates and zoom levels

The Google Maps API breaks up the imagery at each zoom level into a set of
square map tiles arranged in a grid. When a map moves to a new location, or
to a new zoom level, the Maps API determines which tiles are needed and
translates that information into a set of tiles to retrieve.

The tile with coordinates (0,0) is always at the northwest corner of the map,
with x values increasing from west to east and y values increasing from north
to south. Tiles are indexed using x,y coordinates from that origin.

At zoom level 0, the entire world is rendered in a single tile. Each zoom
level increases the magnification by a factor of two. So, at zoom level 1 the
map will be rendered as a 2x2 grid of tiles. At zoom level 2, it's a 4x4 grid.
At zoom level 3, it's an 8x8 grid, and so on.

For example, at zoom level 2 the earth is divided into 16 tiles. Each tile
can be referenced by a unique combination of x, y and zoom:

When creating images for a tile layer, you will need to create an image for
each tile at each zoom level that you wish to support. Google Maps targets
256 dp (device-independent pixels) when displaying tiles. For high resolution
devices, it is recommended that you return high dpi tiles (512x512 px). Refer
to the
Android
Developers documentation for information on supporting different screen
sizes and densities.

Note: The zoom levels supported by the camera depend on various factors,
and are not related to the zoom levels that your tiles will support.

GoogleMap.getMaxZoomLevel() returns the maximum zoom level
available at the current camera position. This takes into account the map
type currently being used. For example, a satellite or terrain map may have
a lower maximum zoom level than the base map tiles.

GoogleMap.getMinZoomLevel() returns the minimum zoom level,
which is the same for every location (unlike the maximum zoom level) but
may vary between devices and map sizes.

Add a tile overlay

The simplest and most common way of creating a tile overlay is to provide a
URL pointing to the relevant tile image.
UrlTileProvider is a partial implementation of
TileProvider that provides image tiles based on a URL. This
class requires that all the images have the same dimensions.

You will need to implement UrlTileProvider.getTileUrl(), which
accepts the tile coordinates (x, y, zoom), and returns a URL pointing to the
image to be used for the tile. The method should return null if there is no
tile for the given x, y and zoom. A URL can point to a web resource, an
Android asset, or a file on the local disk.

Set up your stock of tile images on a server, defined for all the x,y
coordinates and zoom levels that you intend to support. Then add the tile
overlay:

fadeIn: Boolean. Specifies whether the tiles should fade
in. The default value is true. You may find it useful to
turn off the fade-in when switching between tile overlays quickly. For
information on the relationship between transparency and fade-in, see the
section on transparency below.

tileProvider: The TileProvider to use for
this overlay.

transparency: Float. Sets a transparency factor for
tile images. The value must be in the range [0.0f, 1.0f]
where 0.0f means fully opaque (default) and 1.0f
means fully transparent. See the section on
transparency below for a code sample and the
relationship between transparency and fade-in.

visible: Boolean. Specifies the visibility of the tile
overlay. An invisible tile overlay (value false) is not
drawn on the map, but retains all of its other properties. The default
is true.

zIndex: Determines the order in which the tile overlay
will be drawn in relation to other overlays, including
ground overlays
, circles, polylines
and polygons. Overlays with a higher z-index are drawn on top of those
with lower z-indexes. The order of overlays with the same z-index is
arbitrary. The default z-index is 0. Note that
markers are
always drawn above other overlays, regardless of the z-index of the other
overlays.

To see an example of a UrlTileProvider in action, refer to the
TileOverlayDemoActivity in the
sample code
that is bundled with the Google Play services SDK.

Note: If you need more control, you can
define a tile provider by implementing the
TileProvider interface.

Set transparency for tile overlays

It can be useful to overlay transparent tiles on the map, so that users can
see the base map below the overlaid tiles. You can do this by providing your
own transparent tiles, or by setting a transparency factor on the tile overlay
programmatically.

The following code sample toggles the tile overlay's transparency
between 0.5f and 0.0f:

The transparency is implemented as an alpha channel multiplier for tile
images. To set the transparency of a tile overlay, provide a
TileOverlayOptions object with a transparency
in the range [0.0f, 1.0f] as shown in the above sample. A value
of 0.0f means the tile overlay is fully opaque and
1.0f means it's fully transparent. The default value is
0.0f (opaque).

You can access the tile overlay's transparency by calling
TileOverlay.getTransparency(), and you can change it by calling
TileOverlay.setTransparency().

Transparency, animation, and fade-in

There is no animation when the transparency is changed. The transparency
option operates alongside the
fadeIn
option.

Fade-in provides animation of transparency upon tile loading. If you set a
transparency value, the tiles fade in from fully transparent to the defined
transparency value. If you change the transparency during fade-in, the
animation continues toward the new target transparency.

Remove a tile overlay

Clear stale tiles

If the tiles provided by the tile overlay become 'stale', you can call
clearTileCache() to force a refresh. This will cause all the
tiles on this overlay to be reloaded. For example, if the tiles provided by
the TileProvider change, you must call
clearTileCache() afterwards to ensure that the previous tiles are
no longer rendered.